The present invention relates to a novel materials suitable for use as a selective deposition modeling material, particularly in ink jet-type or thermal stereolithography equipment. The novel materials described herein solidify quickly on cooling from a melt to self supporting solids (fast setting) while retaining other physical properties required for ink jet modeling. The modeling material contains a base material that serves as a backbone for the modeling material, a plasticizing component containing at least 10% by weight of at least one plasticizing agent that promotes fast setting and at least one tackifying resin that is compatible with the base material and the plasticizing component. The modeling materials can optionally contain more than 51% by weight of at least one reactive component, wherein at least a portion thereof having fast setting properties.
One of the most significant advances in rapid prototype design has been the development of stereolithography process systems. Other rapid prototype systems of note are laminated object manufacturing (LOM), Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), and 3D Printing. Stereolithography produces prototype parts directly from a vat of reactive resin using three dimensional data to direct an energy source. The energy source cures successive layers of the reactive resin over selected areas to produce the three-dimensional part. Stereolithography systems have in many cases eliminated the need to manufacture tooling for short run or prototype designs and significantly shortened the design and manufacturing cycle. Stereolithography systems, however, require a relatively large vat of reactive resin and an energy source. Due to the cost of the equipment and chemical nature of the resin material, stereolithography systems are generally not practical office accessories. Hence, a relatively unfulfilled group in the field of rapid prototyping are the actual designers working in their offices. Relocating prototype manufacturing from the shop floor to the designer""s office represents the next step in the evolution of rapid prototype design and manufacturing.
At least some selective deposition modeling systems can be used in an office environment to produce a prototype. Selective deposition modeling systems are known. Particular examples of selective deposition systems are the Actua 2100 Multi-jet Modeler system from 3D Systems, Inc., Valencia, Calif.; Genisys(copyright) 3D Printer(trademark) (technology purchased from IBM) from Stratasys Corporation, Minnesota, Z402(trademark), rapid prototyping system from Z-Corporation, Massachusetts, and the Model Maker II from Sanders, New Hampshire. The selective deposition systems described in published PCT patent application (International Publication Number WO 97/11837), which is incorporated herein by reference, to 3D Systems, Inc. is believed to represent said Actua system. In said application, the selective deposition modeling systems are described as including thermal stereolithography.
The patents directed to thermal stereolithography and extrusion modeling equipment contemplate the use of room temperature solid compositions that flow when subjected to elevated temperatures. 3D Systems, for example, discloses in their specifications for thermal stereolithography that the compositions are normally solid at room temperature, but are rendered flowable when heated above their melting points. Suggested materials are thermoplastics, hot-melt glue, wax, and cerro alloys. U.S. Pat. No. 5,695,707, column 4, lines 17-23. IBM discloses in their specifications that an extrusion system can use hot melt adhesives, mixtures of synthetic polymers, wax, resin, metallic alloys, thermoplastic polymers, thermosetting polymers, radiation- or heat-curable polymers, and mixtures thereof. U.S. Pat. No. 5,303,141, columns 6-7 (bridging).
3D Systems further discloses in a published PCT application WO 97/11837 a number of preferred formulations for selective deposition modeling comprising (examples 1-6):
a) paraffin wax having a melting point of 60xc2x0 C. (20-44% by weight); b) a pure monomer hydrocarbon resin comprising a copolymer of xcex1-methylstyrene and vinyl toluene having a viscosity of 1000 centipoise at 130xc2x0 C. and a softening point of 78-95xc2x0 C. (20-50% by weight); c) a medium hard microcrystalline ester wax having a viscosity of 16 centipoise at 100xc2x0 C. and a melting point of 78-86xc2x0 C. (0-12% by weight); d) a hard microcrystalline wax having a viscosity of 16 centipoise at 100xc2x0 C. and a melting point of 93xc2x0 C. (5-10% by weight); e) a soft microcrystalline wax having a viscosity of 13 centipoise at 100xc2x0 C. and a melting point of 69xc2x0 C. (5-20% by weight); f) an ethylene-vinyl acetate copolymer having a viscosity of 575 centipoise at 140xc2x0 C. and a melting point of 92xc2x0 C. (2.3-25% by weight); g) an optional antioxidant (0-2% by weight); h) an optional dioctylphthalate (plasticizer) (0-2% by weight); i) an optional dioctylterephthalate (plasticizer) (0-2.5% by weight); j) an optional antioxidant (0-3% by weight); k) an optional diisononyl phthalate (plasticizer) (0-2% by weight); and 1) an optional dye or coloring compound, not used.
3D Systems discloses in the same published PCT Application an additional preferred composition containing a UV-curable component in example 7 comprising:
a) paraffin wax having a melting point of 60xc2x0 C. (21% by weight); m) a methacrylate terminated polystyrene (51% by weight); c) a medium hard microcrystalline ester wax having a viscosity of 16 centipoise at 100xc2x0 C. and a melting point of 78-86xc2x0 C. (12% by weight); d) a hard microcrystalline wax having a viscosity of 16 centipoise at 100xc2x0 C. and a melting point of 93xc2x0 C. (5% by weight); e) a soft microcrystalline wax having a viscosity of 13 centipoise at 100xc2x0 C. and a melting point of 69xc2x0 C. (5% by weight); f) an ethylene-vinyl acetate copolymer having a viscosity of 575 centipoise at 140xc2x0 C. and a melting point of 92xc2x0 C. (5% by weight); and n) a photoinitiator (1% by weight). No actual physical properties for such a composition or cured article resulting therefrom are provided.
3D Systems discloses in the same published PCT Application an additional preferred composition containing an epoxy resin component (cationically curable) in example 8 comprising:
o) polyethylene oxide having an average molecular weight of 2000 (77% by weight); p) an epoxy novolac oligomer (22% by weight); and q) a cationic photoinitator (1% by weight). No actual physical properties for such a composition or cured article resulting therefrom are provided.
3D Systems discloses in the same published PCT Application an additional preferred composition containing a UV-curable component in example 9 comprising:
n) a photoinitiator (1% by weight); o) polyethylene oxide having an average molecular weight of 2000 (77% by weight); and r) a multifunctional acrylate (22% by weight). No actual physical properties for such a composition or cured article resulting therefrom are provided.
A number of patents have been issued to BPM Technology that are directed to an ink-jet type of modeling systems. The ink jet system employs a piezoelectric jet. Each of the patents suggests that an appropriate build material melts at a temperature from about 50 to 250xc2x0 C., cools quickly and adheres to itself, and has a low rate of shrinkage. A preferred build material comprises a solution of a resin having a hydroxyl number of from about 5 to 100, and a molecular weight greater than about 500, dissolved in at least one primary aromatic sulfonamide. The aromatic sulfonamide allegedly provides the necessary self-adhesion properties. Phenolic resins prepared by the reaction of phenol with formaldehyde are particularly preferred as the resin. The build material can optionally further include antioxidants and flexibilizers.
Ink formulations for ink jet printers are well-known. Such inks, however, are not suitable for selective deposition modeling systems, particularly thermal stereolithography. Conventional ink formulations fail to have sufficient mechanical strength for this purpose. U.S. Pat. No. 5,531,819, assigned to Brother Kogyo, is representative of the teachings in ink jet dyes. The composition, which is solid at room temperature, comprises wax having a melting point between 50 and 130xc2x0 C., a resin, a colorant, and a plasticizer. The composition contains between 30 to about 90% by weight of wax, about 5 to about 70% by weight of a resin having a weight average molecular weight greater than 500, about 1 to 20% by weight of plasticizer, and about 0.1 to 10% by weight of colorant. Examples of suitable resins include polyethylene and ethylene-vinyl acetate copolymer, and mixtures thereof. The plasticizer is most preferably a phthalic acid ester that is liquid at room temperature.
Investment casting materials are also unsuitable for use in selective deposition modeling systems due to their very high viscosity. A representative composition of investment castings is shown in U.S. Pat. No. 5,372,768, assigned to Yates Manufacturing Co. The composition comprises at least about 30% by weight of a thermoplastic material having a viscosity at 200xc2x0 F. of less than about 20,000 centipoise., and, as a filler, at least about 5% by weight of a cross-linked poly(methacrylate). The composition can further include ethylene vinyl acetate or polyethylene to increase the viscosity of the melted material and to increase the hardness and toughness of the solidified material.
Hot melt adhesives are generally not suitable for use in selective deposition modeling systems because the melt viscosities are generally much too high. A representative composition of hot melt adhesives is shown in U.S. Pat. No. 5,750,607, assigned to Shell Oil Company. The compositions comprise a block copolymer having an overall apparent molecular weight in the range of 200,000 to 500,000, a tackifying resin, a plasticizing oil, and a gelling agent, such as a wax, to prevent migration of the plasticizing oil.
Despite the presence of numerous phase change compositions, there is exists a need in the field of selective deposition modeling for a composition having improved strength and toughness. The present invention described hereafter meets this objective and others that will be clear to those skilled in the art.
The present invention relates to a selective deposition modeling material containing a base material, a plasticizing component containing at least 10% by weight of at least one plasticizing agent that is solid at ambient conditions, and at least one tackifying resin that is compatible with the base material and the plasticizing component, wherein the modeling material has a viscosity of less than about 30 centipoise at 130xc2x0 C.
The base material preferably comprises a mixture of long-chain polyolefinic molecules having a number average molecular weight of about 500 to 10,000, more preferably about 4000. The base material preferably comprises a mixture of polyolefinic molecules having sufficient branching that allows long-range chain entanglement and provides interstitial voids for the positioning of plasticizing agents between and amongst adjacent polyolefinic molecules.
The plasticizing component is preferably a mixture of at least one plasticizing agent that is solid at ambient conditions and at least one plasticizing agent that is liquid at ambient conditions.
The tackifying resin is advantageously compatible with the base material and each plasticizing agent in the plasticizing component and acts as a bridge between the base material and plasticizing component to produce a homogenous single-phase solution.
The modeling material of the present invention preferably contains about 50% to 70% by weight of base material, about 8% to 15% of plasticizing component, about 15% to 30% of tackifying resin, and optionally, customary additives with the total amount of the recited components totaling 100% by weight. More preferably, the modeling material contains about 60% to 65% of base material, about 10% to 12% of plasticizing component, about 20% to 25% of tackifying resin, and optionally, customary additives with the total amount of the recited components totaling 100% by weight. Alternatively, the modeling material described herein contains about 60% to 65% of base material, about 10% to 12% of plasticizing component, about 20% to 25% of tackifying resin, and optionally, customary additives with the total amount of the recited components totaling 100% by weight, and wherein the base material contains a mixture of at least one thermoplastic and at least one thermosetting material.
In alternative embodiment, the selective deposition modeling material of the present invention contains about 52% to 98% of a reactive polymeric material that is a mixture of at least one compound containing at least one glycidyl group per molecule, at least one compound having at least one terminal unsaturated group per molecule, at least one compound having at least one vinyl ether group per molecule or mixtures thereof; and a cure agent or activator; and optionally a non-reactive polymeric material or wax material, wherein the modeling material contains a fast set inducing segment content of about 10% to 70% by weight. More preferably, the selective deposition modeling material of the alternative embodiment contains a polyethylene segment content of about 10% to 70% by weight.
The present invention further relates to a method for producing a three-dimensional article by providing a container of a non-reactive solid modeling material described above in communication with a moveable dispensing unit, subjecting at least a portion of the solid modeling material to an elevated temperature in order to produce a flowable liquid material, dispensing said flowable liquid material in desired locations of a platform or regions of a partially formed three dimensional article in order to produce said three-dimensional article.
The present invention further relates to a method for producing a three-dimensional article by providing a container of a reactive solid modeling material described above in communication with a moveable dispensing unit, subjecting at least a portion of the solid modeling material to an elevated temperature in order to produce a flowable liquid material, dispensing said flowable liquid material in desired locations of a platform or regions of a partially formed three-dimensional article in order to produce said three-dimensional article.
The at least partially formed three-dimensional article to a finishing temperature resulting from the non-reactive or reactive-based system can be exposed to a finishing temperature that is greater than the temperature needed to produce a flowable liquid material. Alternatively, the at least partially formed three-dimensional articles can be exposed to ultraviolet radiation in addition to the exposure to a finishing temperature or instead of a finishing temperature
A preferred embodiment of the present invention is the use of the novel hot melt material in a selective deposition modeling system, particularly a thermal stereolithograhy system. The most preferred thermal stereolithography system is available from 3D Systems under the tradename Actua. The present invention, however, is not limited to use solely in such thermal stereolithography systems. Rather, the present invention can be employed in substantially any selective modeling system wherein a phase change material is applied in successive layers as a liquid, and subsequently hardens to produce a three dimensional article.
A conventional thermal stereolithography system is described in U.S. Pat. No. 5,695,707, which is incorporated herein by reference, assigned to 3D Systems, Inc. The system comprises at least one dispensing nozzle coupled to an x-y translation means, at least one flexible tube, a frame, and a moveable platform. The dispensing nozzle(s) is (are) coupled to the x-y translation means, which is coupled to the frame. The dispensing nozzle(s) is (are) coupled to a modeling material container by means of the flexible tube.
The moveable platform is capable of moving vertically relative to the frame, the x-y translation means and dispensing nozzle, via a platform elevator. The x-y translation means and platform elevator are in communication with a control computer, which utilizes, either directly or indirectly, a CAD system or program. Signals from the control computer cause the x-y translation means and platform elevator to move horizontally or vertically, respectively. Together, the control computer, the x-y translation means and platform elevator provide the ability to selectively dispense modeling material to any preselected position on the platform or on a partially formed part on the platform. The resulting three-dimensional article can be subjected to an elevated finishing temperature or light energy as a post-formation step to improve the mechanical and physical properties of the article.
The preferred modeling material is a phase change material or hot melt material that is solid at ambient conditions but melts when subjected to temperatures in excess of about 60xc2x0 C. For purposes of this application, ambient conditions mean a temperature of about 25xc2x0 C. and atmospheric pressure. Additionally, the preferred modeling material has a viscosity in the range of about 10 to 50 centipoise, more preferably in the range of about 10 to 25 centipoise, at its dispensing temperature. A conventional benchmark dispensing temperature is 130xc2x0 C. A preferred modeling material that meets these requirements comprises at least one base material that serves as a backbone for the modeling material and optionally a cure agent or activator, a plasticizing component and a tackifying resin.
The base material is preferably a mixture containing at least one long chain homopolymer and/or copolymer. The chain may be a straight chain, though a branched chain polymer is preferred. The base material can be a thermoplastic or thermosetting material. A thermoplastic material repeatedly softens when subjected to heat. A thermosetting material generally cures to form a hardened material when subjected to heat or other curing conditions. Mixtures of thermoplastic and theromosetting materials can be used.
A preferred thermoplastic material suitable for the present invention is solid at ambient conditions but forms a flowable liquid when subjected to temperatures in excess of about 60xc2x0 C., more preferably in excess of about 70xc2x0 C. The thermoplastic material preferably exhibits low volume shrinkage during the phase change from a liquid to a solid. More preferably, the volume shrinkage is less than about 15%, most preferably less than about 10%.
Commercial thermoplastic materials useful in this application can be copolymers. Copolymers suitable for use in the present invention can contain alternating, random, or block monomeric units. The monomeric units are preferably derived from aromatic compounds that can be substituted with alkyl, alkoxy, alkenyl, or halogen groups. The advantage of a coploymer is that the physical properties of the overall polymeric molecule and formulation thereof can be varied by modifying the type and ratio of monomers. Particularly preferred monomeric units are styrene and methyl styrene. Such copolymers have relatively good mechanical properties at low molecular weights and therefore have useable melt viscosities. Examples of preferred copolymers based upon mixtures of styrene and methyl styrene include Picotex LC, Kristalex 3085, Picolastic A75 and Picotex 75, which are commercially available from Hercules Chemical Company. Other suitable copolymers include aliphatic/aromatic mixed copolymers, such as Hercolite 2100, commercially available from Hercules, hydrogenated styrenic-based copolymers, such as Regalrez 1094, commercially available from Hercules, amide-urethanes, commercially available from UnionCamp, Wayne, N.J., block copolymers of styrene and butadiene, such as Kraton G 1652, commercially available from Shell, Houston, Tex., and ethylene-carbon monoxide copolymers (A-C 830, commercially available from AlliedSignal).
Examples of suitable homopolymeric materials are polyolefins, such as polyethylene (A-C 6, commercially available from AlliedSignal, Morristown, N.J. and Epolene N-14, commercially available from Eastman), polyamides (X37-523-235 and X37-4978-70, commercially available from UnionCamp), polypropylene, polybutylene, polyisobutylene and mixtures thereof. Polyethylene is most preferred.
The base material particularly suitable for use herein has a number average molecular weight greater than about 500 and less than about 10,000, more preferably the base material has a number average molecular weight greater than about 2500 and less than about 5000, most preferably about 4000. Polymeric materials suitable for this application have melt viscosities between 100 and 5000 centipoise at 130xc2x0 C. Polymeric materials having a viscosity greater than about 5000 centipoise can be added only at such small percentages as to only make insignificant contributions to the properties of the overall modeling material.
In an alternative embodiment, the base material can be based in whole or in part on a reactive polymeric material, particularly a thermosetting material. The preferred reactive polymeric material reacts when subjected to elevated temperatures, ultraviolet radiation, or contacted by a curing agent. Epoxy resins, for example, cure when subjected to heat, ultraviolet radiation or activated with a curing agent. For this application, the epoxy resin should not be activated when subjected to conventional ink dispensing conditions in order to avoid premature curing. Examples of conventional curing agents are primary and secondary amines, which can be catalyzed by tertiary amines and/or imidazole, anhydrides, and Lewis acids. Ethylenically unsaturated compounds cure when subjected to ultraviolet energy, particularly when photoinitiators are present. Suitable unsaturated compounds include (meth)acrylate, di(meth)acrylates, vinyl ether monomer, and allyl monomers. Preferably, the reactive material contains an epoxy resin, vinyl ether and/or (meth)acrylate that cures when subjected to ultraviolet radiation.
The reactive polymeric material is preferably composed of a primary reactive material, a reactive modifier material, and optional customary additives. The primary reactive material, preferably about 40 to 80% by weight of the reactive material, must have good phase change properties that are discussed more fully below. The reactive modifier material, preferably about 20 to 60% by weight of the reactive material, modifies the ultimate cured physical properties. A wide range of reactive monomers are suitable modifier materials. Although the modifier material can be selected primarily on the basis of cured physical properties, compounds with poor phase change properties, such as liquids at room temperature, can only be used in limited concentrations. The customary additives include free radical stabilizers, such as Irganox 3052, and thermal stabilizers, such as Irganox 1010, which are both commercially available from Ciba Specialty Chemicals Corporation.
For the reactive formulations, a fast set inducing segment is included in the molecule of one or more primary reactive materials. Addition of the fast set inducing segment, such as polyethylene, is necessary because the vast majority of commercially available monomers are liquids or tend to super cool before solidifying. Preferably, the overall reactive modeling material has a fast set inducing segment content of about 10% to 70% by weight, more preferably about 15 to 40% by weight. For example, the reactive component in Example 9 was prepared by reacting 59 parts by weight polyethylene monoalcohol with 24 parts diisocyanate and 17 parts hydroxy methacrylate. The resulting reactive component is composed of 59% fast setting segments. Selective deposition composition Example 12 uses 70% of reactive component Example 9 and therefore has 41% (0.59xc3x970.70) fast setting segments. Other polymer segments with fast set properties are possible although high melting point or highly polar segments would lead to undesirably high viscosities. Polyethylene oxide is an example of a polymer with high crystallinity but relatively low melt viscosity.
Table 1 below shows the set times for several commercially available reactive solids compared with Example 13 of this invention. Solid reactive compounds tend to either super cool or crystallize to polycrystalline masses with very little cohesion. Example 13 contains 69% of a monomer which that 30% by weight of a polyethylene segment for a 21% polyethylene segment content overall.
Particularly preferred primary reactive polymeric materials for this application are solid acrylate or methacrylate derivatives of polyethylene (C18 to C50), more preferably C18 to C36. A particularly preferred material is commercially available from Sartomer Company, Exton, Pa., under the tradename and SR 257 (stearyl acrylate) (C18). Polyethylene mono or diols, although not by themselves reactive, copolymerize with epoxy monomers and thus can constitute a primary reactive polymer in cationic epoxy formulations. Unilin 425 from Baker Petrolite, Tulsa, Okla. is a preferred example of such a polyethylene monoalcohol. Solid vinyl ether monomer is available from AlliedSignal. A preferred example of a vinyl ether monomer is Vectomer 4210.
The reactive modifier material should preferably be solid and have a melting point between about 50 and 100xc2x0 C. A preferred acrylate monomer is CD 406, Sartomer, which melts at 75-80xc2x0 C. A preferred reactive modifier containing at least one glycidyl group is a difunctional cycloaliphatic carboxylate epoxy, CY 179, commercially available from Ciba Specialty Chemicals Corporation.
The reactive modeling material comprises, in addition to the base material, a photoinitiator and optionally an accelerator. The photoinitiator is present at about 0.2% to about 2% by weight. The selected photoinitator is preferably optimized to maximize absorbance at the operational wavelength of the selected UV transmitter. Particularly preferred photoinitiators are Irgacure 184 or Irgacure 819 (Ciba Specialty Chemicals Corporation), Lucirin (BASF AG, Mount Olive, N.J.), and UVI 6974 (Union Carbide). Many other suitable photoinitiators are well-known and commercially available.
The reactive modeling material can optionally contain other customary additives, such as antioxidants, antifoaming agents, thixotropic agents, fillers and coloring agents to suit particular applications. Such additives must be incorporated into the modeling materials in such a manner that the resulting mixtures have an appropriate viscosity at the dispensing temperature for the selective deposition system.
In the reactive embodiment described above, the modeling material preferably contains in excess of 50% by weight of the reactive polymeric material, more preferably in excess of about 85% by weight, up to about 98% by weight, with the balance being a cure agent or activator or accelerator and optionally, at least one wax material and/or a non-reactive polymeric material.
In the embodiment utilizing a reactive polymeric material, Applicants discovered that the most advantageous properties are obtained by using a modeling material containing more than 50% by weight of the reactive polymeric material. However, in order to achieve such a high of level of reactive material and still retain properties suitable for phase change part building, the reactive polymeric material must behave in manner similar to mixtures of thermoplastics and paraffins. In other words, the reactive polymeric material must cool quickly to a reasonably hard solid, which corresponds to a xe2x80x9cwax-likexe2x80x9d solidification behavior. The particularly preferred reactive polymeric materials described above satisfy these requirements.
In a more preferred embodiment, the base material contains a mixture of at least one non-reactive polymeric material and at least one natural or synthetic wax. Examples of such waxes include paraffin wax and microcrystalline wax, wax of plant origin, such as, candellia wax, carnuba wax, rice wax or hohoba solid wax, wax of animal origin, mineral wax, synthesized hydrocarbon Fischer-Tropsch wax or polyethylene wax, hydrogenated wax, hardened castor oil or derivatives thereof, modified wax, montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives or polyethylene wax derivatives, polymer wax. The waxes may be used alone, or preferably as a mixture. Waxes suitable for the present application have low melt viscosities (1-10 centipoise at 130xc2x0 C.) in order to offset the higher viscosity of the support materials. The selected waxes must also cause the modeling material to solidify quickly to a pliable microcrystalline solid. Many organic materials with otherwise suitable melting points and viscosities solidify to crystalline solids with large and disruptive crystalline forms and have little cohesion between crystals. Other materials, such as sorbitol, tend to super cool to a sticky viscous liquid, which transforms over hours or days to a hard glassy solid. Neither of these alternative hardening behaviors is suitable for ink jet modeling.
The base material in the non-reactive modeling material contains about 50% by weight to about 70% by weight of at least one wax material with the balance being the non-reactive polymeric material(s) described above.
The plasticizing component provides flexibility and toughness to the hardened article by moderating the packing forces between polymeric chains as well as influencing the set time. Suitable plasticizers may be, for example, an aliphatic ester, an aromatic ester, a phosphoric acid ester, an oxyacid ester, a phthalic acid ester, an aliphatic acid ester, a polyester type plasticizer, an epoxy type plasticizer and a trimetallic acid type plasticizer. A particularly preferred plasticizer component contains at least one plasticizing agent that is solid at ambient conditions. More preferably, the plasticizer component is a mixture comprising at least one plasticizing agent that is solid under ambient conditions and at least one plasticizing agent that is liquid at ambient conditions. The addition of a solid plasticizer mitigates the tendency of plasticizers to promote undesirable supercooling characteristics as described above.
The at least one solid plasticizing agent is preferably an aromatic or cycloaliphatic-based phthalate, particularly diphenyl- or dicyclohexyl-phthalate. Preferably, said solid plasticizing agent is dicyclohexylphthalate or dibenzylphthalate, which is commercially available as Morflex 150 from Moreflex Inc. (Greensboro, N.C.), or 1,4-cyclohexane dimethanol dibenzoate, which is commercially available as Benzoflex 352 from Elsicol Chemical Corporation (Rosemont, Ill.), or diphenylisophthalate, which is commercially available from Aldrich Chemical Company (Milwaukee, Wis.).
The at least one liquid plasticizing agent is preferably an alkyl benzyl phthalate or alkyl aryl phosphate ester. Examples of suitable liquid plasticizing agents are Santicizer 278 and Santicizer 2148, which are commercially available from Solutia, St. Louis, Mo.
The plasticizing component contains at least about 10% by weight of at least one plasticizing agent that is solid at ambient temperatures. Modeling materials containing less than about 10% by weight of solid plasticizing agent exhibit unacceptably reduced flexibility when sufficient plasticizing component is added to improve flexibility. The upper limit on the amount of solid plasticizing agent is governed by the: 1) overall viscosity of the modeling material, which must have a viscosity of about 20-25 centipoise at the dispensing temperature; and 2) hardness which falls off at high plasticizer content.
The significance of the selected plasticizer is illustrated (Table 1, below) by comparing the set times of 1:1 mixtures of a base polymer, Regalite R101 (Hercules, Wilmington, Del.) with various plasticizers. The addition of a fast set plasticizer can also lead to other desirable properties of increased flexibility of the solid and decreased viscosity of the melt. However, the improved properties must be balanced against reduced hardness at higher plasticizer levels. The fastest set time in the table is for Benzoflex 352, which is a tested solid with the highest melting point. Santicizer 278 shows a decrease in set time over paraffin despite being a room temperature liquid. Morflex 150, a relatively low melting solid, shows a dramatic increase in set time. The conclusion to be draw from these results is that it is possible to achieve a good balance between set time and mechanical properties at plasticizer levels which would conventionally be considered very high.
The non-reactive modeling material contains at least one tackifying resin that is compatible with both the base material and the plasticizing component. The tackifying resin acts as a bridge between components of differing polarities and solubilities in order to produce a homogenous single-phase solution. The preferred base materials described above are soluble in aromatic solvents and have a MMAP cloud point less than 80xc2x0 C. (MMAP is 1:2 mixture of methylcyclohexane and aniline) and have a polarity measured by DACP cloud point of less than 42xc2x0 C. (DACP; 1:1 mixture of xylene and 4-hydroxy-4-methyl-2-pentanone). A low MMAP cloud point indicates that the material is more aromatic character. A low DACP indicates higher polarity. An alternative measure of solubility for aromatic resins is OMS cloud point (OMS means odorless mineral spirits). The OMS cloud point should be below the melting point of the formulation, which is preferably in the range of 50-75xc2x0 C. The preferred plasticizing component is soluble in both MMAP and OMS and has a high polarity of indicated by a DACP cloud point of less than xe2x88x9230xc2x0 C. Escorez 5320, from Exxon Chemical Company, Floral 85 and Floral 105, from Hercules are particularly preferred tackifying resins.
The non-reactive modeling material can optionally contain other customary additives, such as antioxidants, antifoaming agents, thixotropic agents, fillers and coloring agents to suit particular applications. Such additives must be incorporated into the modeling materials in such a manner that the resulting mixtures have an appropriate viscosity at the dispensing temperature for the selective deposition system.
The non-reactive modeling material preferably contains about 50% to 70% by weight, more preferably about 60% to 65% of base material, about 8% to 15%, more preferably about 10% to 12% of plasticizing agent, and about 15% to 30%, more preferably about 20% to 25% of tackifying resin, with the total amount of such components and the optional customary additives totaling 100% by weight.
Without intending to be bound to any particular theory, the base material serves as a backbone for the modeling material as it cools by beginning to gel and encapsulating the remaining components within a fixed volume. Once the modeling material has cooled, the base material is the primary contributor to the mechanical properties of the hardened article. An important aspect of this invention is the provision of a long-chain polymeric material, which upon solidification, allows a plasticizing agent to be located in the interstitial spaces amongst and between adjacent polymeric molecules. A polymeric material having at least some branching is particularly preferred in order to permit long range chain entanglement. Such chain entanglement allows the addition of a sufficient level of plasticizer to impart flexibility without causing a significant decrease in strength.
Modeling materials for ink jet solid modeling must quickly form a hard solid on cooling, which is in contrast to materials that super cool to viscous liquids and may require many hours to fully solidify. A super cooled liquid would not be able to hold its shape as additional layers are printed. The property of quickly forming a solid with useful mechanical properties is called xe2x80x9cfast setxe2x80x9d in the hot melt adhesives field. In the novel materials described herein, the desired fast set property is achieved in one of two ways. For the non-reactive formulations, a plasticizer, typically a room temperature crystalline solid, is incorporated into the compositions. The selected plasticizer counteracts the tendency of the composition to super cool due to the presence of flexible, non-crystalline components.
The preferred reactive and non-reactive modeling materials described above can be formulated by combining the desired components in a stainless steel kettle having a heating source and stirring mechanism. The kettle is heated to a temperature of 130xc2x0 C. while stirring the components at a rate of 20-60 rpm using a mechanical blade stirrer. The stirring at an elevated temperature is continued until a clear homogenous solution is obtained. The molten material is then filtered and then poured into a dispensing container. The dispensing containing is then affixed to a selective deposition modeling system as described above wherein the modeling material is liquefied and dispensed at preselected positions to produce a three-dimensional article.
The modeling material is dispensed through the nozzle which has an outlet having a particular size, which can vary based upon application. The modeling material, which is a solid at room temperature and pressure, must be heated to above its melting point. The modeling material should have a viscosity of less than 50 centipoise at the dispensing temperature. The liquefied modeling material can be dispensed by applying air pressure or by the force of gravity. The flow of such modeling material can be interrupted by means of a valve at the end of the nozzle or by removing the pressure.